Many plants for electrolytic treatment of metal strips are known, in which the strip is caused to travel at a high speed in front of an electrode placed at a certain distance from the strip, while an electrolytic liquid fills the space between the strip and the electrode. By placing the strip and the electrode at different potentials, an electric current may be passed through the space filled with the electrolytic liquid to produce an electrolysis effect. In some plants used for pickling or cleaning metal strips, this electrolysis effect produces a release of bubbles which promotes the detachment of a surface film from the strip.
To enable the electrolysis to be carried out under proper conditions, the gap between the strip and the electrode, through which the electric current passes, must be as narrow as possible but, in the event of a fault in the tension drive or bad flatness of the strip, the latter may come into frictional contact with the surface of the facing electrode, and this may cause damage to the strip and/or the electrodes.
In some known plants, in order to maintain the strip in a constant distance from the electrode, the latter consists of a roll placed in contact with the strip. The roll consists on its periphery of a conductive wall covered with a noncontinuous insulating coating of a constant thickness, in which recesses are provided, so that the entire surface of the roll consists of bearing sections of a constant height, which are separated from each other by spaces allowing the conductive wall of the roll to be seen; the electrolytic liquid is injected into the spaces provided in this way to produce the electrolysis between the strip and the conductive wall of the roll, which are at different potentials. In these known plants, the electrode-roll is always placed outside the electrolytic bath. In some cases, the liquid is conveyed directly from the bath to the electrode roll by the previously submerged strip or by a carrier roll dipped in the bath and placed in contact with the electrode-roll. In other cases, the strip passes over rolls which are offset in height and define a zigzag path, the liquid being injected into the dihedrally-shaped spaces provided between the upstream length of the strip and each roll.
Arrangements of this kind do not permit a large quantity of liquid to be conveyed onto the electrode-roll, nor to be removed from the latter, which would be particularly useful in the case of a pickling or cleaning or dechroming treatment.
In addition, it is not easy, without making the plant more complex, to obtain a homogeneous effect of the treatment in the direction of travel, nor to carry out the treatment on both faces.
Lastly, the speed of travel is relatively limited because, commencing at a certain speed, a lateral floating of the strip may take place, which is due to what is known as the aquaplaning effect, which makes it difficult to guide the strip and disturbs the transverse homogeneity of the treatment.